The present invention relates generally to water-blocking yarns. In especially preferred embodiments, the present invention relates to telecommunications cables (e.g., optical fiber cables) which include a multifilament water-blocking yarn.
Telecommunications cables have traditionally been provided with internal components which serve to minimize entry and migration of water which could catastrophically damage electronics connected to the cable as well as the cable itself. In this regard, the interstices within the cables have previously been flooded with a petrogel filler compound in an effort to minimize water entry and migration. More recently, superabsorbant polymers (SAP) have been employed for such purposes. See generally, Bringuier et al, Reliability of Dry Waterblocking Materials, EuroWire, pp. E60-E64 (March 1999), Patel, Functional Performance of Ocean Water-Blocking Tapes, EuroWire, pp. E94-E97 (September 1999), and Czupryna, Water Blocking Yarns and Tapes, Wire and Cable Technology International, pp. 43-44 (November 1999).1 
1 The entire content of each cited printed publication and U.S. Patent is hereby expressly incorporated herein. 
Recently, U.S. Pat. Nos. 5,264,251 and 5,342,686 disclose aramid yarns coated with SAP that may be employed in optical communications cables. U.S. Pat. No. 5,817,713 discloses water-swellable fiber coatings whereby the coatings are semi-gel dispersions of SAP in a polyvinyl chloride plastisol. The dispersion may then be applied as a coating onto a fiber substrate and then heat cured to the semi-gel state. U.S. Pat. No. 5,543,215 discloses SAP particles bound to cellulosic fibers by means of a water-soluble polymeric binder having hydrogen bonding functionality or coordinate covalent bond forming functionality on each repeating unit of the polymer.
While the prior proposals have advanced the art of water-blocked cables to some extent, continual improvement is sought. Particularly, solutions to provide enhanced water-blocking functions for telecommunications cables (i.e. higher absorption capacity as well as faster swell rates) without appreciably increasing the size and/or weight of the finished cable are especially desired. It is towards fulfilling such solutions that the present invention is directed.
Broadly, the present invention is embodied in synthetic polymeric filaments containing SAP particles adhered to the filament surfaces by a nylon binder which is soluble in alcohols (e.g., lower C1-C3 aliphatic alcohols). Such SAP-coated filaments may then be incorporated into telecommunications cables as a component part thereof to achieve enhanced water-blocking functions. In preferred embodiments, the SAP particles include homopolymers, copolymers, and/or mixtures of sodium and potassium polyacrylates, starch grafted sodium polyacrylates and partial sodium salts of polypropenoic acid which are bound to the yarn surfaces by the nylon binder.
Most preferably, the coated multifilamentary yarns of the present invention are made by bringing an uncoated yarn into contact with a nonaqueous liquid coating material comprised of the nylon binder dissolved in an alcohol solvent containing a dispersion of the SAP particles for a time sufficient to coat the yarn with the liquid coating material. Thereafter, the xe2x80x9cwetxe2x80x9d coated yarn is dried at an elevated temperature above the melting point of the nylon binder but below the melting point of the SAP particles for a time sufficient to evaporate the alcohol solvent. The SAP particles will therefore be bound to the yarn surfaces by the residue of the nylon binder that remains following drying.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.